This invention relates to an improved centrifugation method for separating a polyhalogenated product from product centrate or filtrate.
In the production of polyhalogenated flame retardants, well known centrifugation or filtration techniques are typically used to separate the product from the reaction mass and/or slurry containing the product once the halogenation reaction is complete. Typically, the product is a solid which is suspended as a slurry in the reaction mass solvent. Accordingly, the centrifugation cycle should be sufficient to separate the product from the slurry substantially as it is produced without excessive amount of down time for centrifuge cleaning or centrifuge filter cloth replacement. However, due to the particular characteristics of the product and/or slurry being centrifuged, the length of the centrifugation cycle and the number of centrifugation cycles may suffer considerably due to decrease in the porosity of the centrifuge filter cloth. When the filter cloth porosity decreases substantially, centrifugation of the product may decrease to an unacceptable rate. At this point, centrifugation is terminated and corrective action taken. Typically, the appropriate corrective action is changing the filter cloth in order to again increase the product throughput to an acceptable rate. Depending on the size and complexity of the centrifugation equipment, cloth replacement may be quite costly in terms of actual expense and with respect to decrease in production rates. There is a need therefore for a facile economic means for extending the centrifugation cycle for polyhalogenated products in order to decrease the amount of centrifuge down time. For the purposes of this invention, whenever centrifugation is referred to, centrifugation and filtration are contemplated and whenever the term "centrifugation cycle" is used it refers to the number of batches of product that can be centrifuged or a predetermined amount of product that is centrifuged.